1. Field of the Invention
The present invention relates to a thin film magnetic head and a method of manufacturing the same, particularly to an inductive type writing magnetic transducing element and a method of manufacturing the same.
2. Description of the Related Art
Recently a surface recording density of a hard disc device has been improved, and it has been required to develop a thin film magnetic head having an improved performance accordingly. A hybrid or composite or combination type thin film magnetic head is constructed by stacking, on a substrate, an inductive type thin film magnetic head intended for writing and a magnetoresistive type thin film magnetic head intended for reading, and has been practically used. In general, as a reading magnetoresistive element, an element utilizing anisotropic magnetoresistive (AMR) effect has been used so far, but there has been further developed a GMR reproducing element utilizing a giant magnetoresistive (GMR) effect having a resistance change ratio higher than that of the normal anisotropic magnetoresistive effect by several times. In the present specification, elements exhibiting a magnetoresistive effect such as AMR and GMR reproducing elements are termed as a magnetoresistive reproducing element or MR reproducing element.
By using the AMR reproducing element, a very high surface recording density of several gigabits/inch.sup.2 has been realized, and a surface recording density can be further increased by using the GMR element. By increasing a surface recording density in this manner, it is possible to realize a hard disc device which has a very large storage capacity of more than 10 gigabytes.
A height (MR Height: MRH) of a magnetoresistive reproducing element is one of factors which determine a performance of a reproducing head including a magnetoresistive reproducing element. The MR height MRH is a distance measured from an air bearing surface on which one edge of the magnetoresistive reproducing element is exposed to the other edge of the element remote from the air bearing surface. During a manufacturing process of the magnetic head, a desired MR height MRH can be obtained by controlling an amount of polishing the air bearing surface.
At the same time, the performance of the recording magnetic head is also required to be improved in accordance with the improvement of the performance of the reproducing magnetic head. In order to increase a surface recording density, it is necessary to make a track density on a magnetic record medium as high as possible. For this purpose, a width of a write gap at the air bearing surface has to be reduced to a value within a range from several micron meters to several sub-micron meters. In order to satisfy such a requirement, the semiconductor manufacturing process has been adopted for manufacturing the thin film magnetic head.
One of factors determining the performance of the inductive type thin film writing magnetic head is a throat height (TH). This throat height is a distance of a pole portion measured from the air bearing surface to an edge of an insulating layer which serves to separate a thin film coil from the air bearing surface. It has been required to shorten this distance as small as possible. The reduction of this throat height is also decided by an amount of polishing the air bearing surface.
In order to improve the performance of the inductive type thin film writing magnetic head, there has been proposed to reduce a length of portions of the bottom pole and top pole surrounding the thin film coil (in the present specification, said length is termed as magnetic path length).
FIGS. 1-8 show successive steps for manufacturing a conventional typical inductive type thin film magnetic head, these drawings showing a cross-sectional view cut along a line perpendicular to the air bearing surface. It should be noted that in this combination type thin film magnetic head, the inductive type thin film magnetic head for writing is stacked on the reproducing MR element.
First of all, as shown in FIG. 1, an insulating layer 2 consisting of, for example alumina (Al.sub.2 O.sub.3) and having a thickness of about 5-10 .mu.m is deposited on a substance 1 made of a non-magnetic and electrically insulating material such as aluminum-titanium-carbon (AlTiC). A bottom shield layer 3 constituting a magnetic shield which protects the GMR reproducting element of the reproducing head from the influence of an external magnetic field, is formed with a thickness of 3-4 .mu.m. Next, a GMR layer 5 having a thickness of several tens nano meters is formed on the bottom shield such that the GMR layer is embedded in a shield gap layer 4. Then, a magnetic layer 6 made of a permalloy is formed with a film thickness of 3-4 .mu.m. This magnetic layer 6 has not only the function of the upper shield layer which magnetically shields the GMR reproducing element together with the above described lower shield layer 3, but also has the function of a bottom pole of the writing thin film magnetic head. Here, for sake of explanation, the magnetic layer 6 is called a first magnetic layer by taking into account the fact that this magnetic layer constitutes one of the poles of the writing magnetic head.
Then, as shown in FIG. 2, a write gap layer 7 made of a non-magnetic material such as alumina and having a thickness of about 200 nm is formed on the first magnetic layer 6. A photoresist 8 is formed on the write gap layer 7 at an area except for a potion corresponding to the pole portion to be formed later, said photoresist determining a reference position for the throat height. Next, a thin copper layer 9 having a thickness of about 100 nm is formed on a whole surface by sputtering. Thin copper layer 9 constitutes a seed layer for the formation of the thin film coil by electroplating. Therefore, this layer is also called a seed layer. On the seed layer 9, is formed a thick photoresist 10 having a thickness of 3 .mu.m, and an opening 11 is formed within the photoresist 10 such that the seed layer is exposed at the bottom of the opening. A height of this opening is equal to a thickness of the photoresist and is 2 .mu.m, and a width of the opening is also 2 .mu.m.
Next, an electroplating of copper is performed using a plating bath consisting of a copper sulfate to form first layer thin film coil windings 12 having a thickness of 2-3 .mu.m within the opening 11 formed in the photoresist 10 as depicted in FIG. 3. It is preferable that a thickness of the coil winding 12 is smaller than a depth of the opening 11.
Then, as illustrated in FIG. 4, after removing the photoresist 10, a milling with an argon ion beam is carried out to remove the seed layer 9 as shown in FIG. 5 to separate the successive coil windings 12 to form a single coiled conductor. During this ion beam milling, in order that the seed layer 9 at roots of the coil windings 12 of the thin film coil is not remained, the ion beam milling is performed at an angle of 5-10.degree.. In this manner, by conducting the ion beam milling substantially at right angles, debris of the material of the seed layer 9 are liable to be adhered to the coil windings 12. Therefore, it is necessary to increase a distance between successive coil windings.
Next, as depicted in FIG. 6, a photoresist 13 is formed to cover the coil windings 12 of the first layer thin film coil, and after polishing the top surface thereof into a flat surface, coil windings 15 of a second layer thin film coil are formed on a seed layer 14 by a similar method as that described above. Furthermore, after forming a photoresist 16, a second magnetic layer 17 made of a permalloy and having a thickness of 3-5 .mu.m is formed, said second magnetic layer constituting the top pole.
Then, as shown in FIGS. 7 and 8, parts of the write gap layer 7 and first magnetic layer 6 are etched while a pole portion 17a of the second magnetic layer 17 is used as a mask, to form a trim structure. Furthermore, an overcoat layer 18 made of an alumina is formed on a whole surface. It should be noted that FIG. 8 is a cross sectional view cut along a line 8--8 in FIG. 7, and first and second shield gap layers 4a and 4b constituting the shield gap layer 4 which electrically isolates and magnetically shields the GMR element 5 are also shown together with conductive layers 5a and 5b constituting the electric connection to the GMR element.
In an actual method of manufacturing the thin film magnetic head, after forming a large number of the above mentioned structures in a single wafer, the wafer is divided into bars in each of which a number of thin film magnetic heads are aligned, and a side wall of a bar is polished to obtain an air bearing surface 19 (refer to FIG. 7). During the formation of the air bearing surface 19, the GMR layer 5 is also polished, and a combination type thin film magnetic head having a desired throat height and MR height can be obtained. Furthermore, in an actual thin film magnetic head, electric conductors and contact pads for performing the electrical connection to the thin film coils 12, 15 and MR reproduction element are formed, but they are not shown in the drawings.
As shown in FIG. 7, an angle .theta. (apex Angle) between a line S connecting side corners of the photoresist layers 11,13,15 for isolating the thin film coils 12,14 and the upper surface of the third magnetic layers 16 is an important factor for determining the performance of the thin film magnetic head together with the above described throat height TH and MR height.
Moreover, as shown in FIG. 8, a width W of a pole portion 6a of the trim structure and the pole portion 17a of the second magnetic layer 17 determines a width of tracks formed on a magnetic record medium. Therefore, in order to realize a higher surface recording density, this width W has to be thin as small as possible.
In the conventional combination type thin film magnetic head manufactured in the manner explained above, there is a problem particularly in a point of a miniaturization of the inductive type recording thin film magnetic head. It has been known that characteristics of the inductive type thin film magnetic head such as magnetic flux rising time, non-linear transition shift (NLTS) and over-write property can be improved by decreasing a magnetic path length L.sub.M which is a length of portions of the first and second magnetic layers 6 and 17 which surround the coil windings 12, 15 of the thin film coil. In order to reduce this magnetic path length L.sub.M, it is necessary to reduce a coil width L.sub.C of portions of the coil windings 12, 15 surrounded by the first and second magnetic layers 6 and 17. However, as will be explained hereinafter, in the known thin film magnetic head, said coil width L.sub.C could not be shortened.
In order to reduce the coil width L.sub.C of the inductive type thin film magnetic head, it is necessary to reduce a width of respective coil windings of the thin film coil as well as a distance between successive coil windings. However, a reduction in a width of the coil windings is limited by a fact that the thin film coil should have a low resistance. That is to say, in order to reduce the resistance of the thin film coil, the thin film coil is made of a copper having a high electric conductivity, but since a height of the thin film coil is limited to 2-3 .mu.m, a width of the coil windings could not be smaller than 1.5 .mu.m. Therefore, in order to reduce the coil width L.sub.C, it is necessary to reduce a distance between successive coil windings.
However, in the known thin film magnetic head, the distance between successive coil windings 12, 15 could not be reduced. Now reasons thereof will be explained.
As stated above, the coil windings 12, 15 of the thin film coil are formed by the electroplating of a copper. In this case, in order to deposit a copper within the openings 11 uniformly over a whole wafer surface, the seed layer 9 having a thickness of 100 nm is formed, and after forming the coil windings 12, 15 by depositing a copper selectively within the openings 11 at which the seed layer 9 is exposed by electroplating, the seed layer 9 is selectively removed in order to separate successive coil windings from each other. This removal of the seed layer 9 is carried out by the ion beam milling using, for instance an argon ion beam, while the coil windings 12, 15 are used as a mask.
Here, in order to remove the seed layer 9 between successive coil windings 12, 15 sufficiently, it is preferable to perform the ion beam milling at right angles to the surface of the substrate. However, then debris of etched copper might be adhered to the coil windings and the electrical isolation between successive coil windings might be broken. Therefore, a distance between successive coil windings could not be narrowed.
In order to mitigate the above problem, the ion beam milling may be performed with an angle of 5-10.degree.. Then, a portion behind the photoresist 10 could not be sufficiently irradiated with the ion beam and the seed layer 9 might be remained partially. Therefore, in order to avoid the breakage of the electrical isolation between successive coil windings 12, 15, a distance between successive coil windings could not be small. In the conventional thin film magnetic head, a distance between successive coil windings has to be long such as 2-3 .mu.m and could not be made narrower than this value.
When the thin film coil 12, 15 is formed by the electroplating as stated above, it is necessary to stir the plating bath such as a copper sulfate in order to attain a uniform thickness of the thin film coil. When a width of walls defining the openings 11 formed in the photoresist 10 is thinned, the thin walls might be destroyed by stirring the electrolytic solution and the thin film coil could be no more formed accurately. In this manner, in the known thin film magnetic head, a distance between successive coil windings could not be reduced.
Moreover, in the known thin film magnetic head, the photoresist 8 is formed such that the reference position of the throat height, i.e. a throat height zero position is defined by the photoresist. After forming the first layer thin film coil 12, the photoresist 8 is also etched during the etching process for removing the seed layer 9 and an edge of the photoresist 8 is retarded. Therefore, in a completed thin film magnetic head, it is impossible to obtain the throat height having a desired value. This is one of factors which decrease a manufacturing yield of the thin film magnetic head.
In order to improve NLTS property of the inductive type thin film magnetic head, the number of coil windings of the thin film coil may be increased. However, for this purpose, the number of thin film coil layers has to be increased such as four or five layers. Then, the apex angle might be increased and a narrow track width could not be attained any more. In order to keep the apex angle within a given range, it is desired to limit the number of thin film coil layers to be not larger than three, preferably not larger than two. Then, the number of the coil windings could not be increased, and therefore NLTS property could not be improved.